Heretofore, low molecular weight polymers, for example, low molecular weight polyolefins such as polyethylene and polypropylene have been widely used as waxes in a variety of applications, for example, such as pigment dispersants, rubber processing aids, resin processing aids, additives to ink and coating compositions, fiber treating agents, and electrostatographic toners. In the recent years, the demand for such low molecular weight polymers in these applications is increasing and more strict requirements are imposed on their quality.
Known methods for producing low molecular weight polyolefins include telomerization of olefins, thermal degradation of high molecular weight polymers, and separation and purification of low molecular weight polymers by-produced during the preparation of high molecular weight polymers.
However, the previously proposed processes based on thermal degradation suffer from several problems in that the size of reactor is increased when a tank type reactor is used for batchwise mass production, and that control of reaction conditions such as temperature is difficult when a tubular reactor is used.
In the pyrolytic processes, volatile components including low molecular weight hydrocarbons are produced during pyrolysis of polyolefins, and if such volatile components, even in minor amounts, are left in the final product of pyrolytic wax, the pyrolytic wax becomes deteriorated in quality with respect to residual volatile content, smell, flash point, molecular weight distribution and the like. Further, the low molecular weight hydrocarbons can be oxidized with air entrained with the polyolefin feed and air incidentally admitted on the way of the process to thereby produce oxygenated hydrocarbons which will adversely affect the hue of the pyrolytic wax product, and the degree of separation of such hydrocarbons varies among separating techniques. It is thus necessary to effectively remove the volatile components in the production process.
Moreover, since the thermal degradation processes generally use severe reaction conditions, it is likely that low molecular weight fractions of the resulting polyolefin have poor hue due to thermal history and thermally deteriorated contaminants are formed in the reactor, and consequently, a continuous mode of production is difficult. To overcome this problem, a method of carrying out pyrolysis in the presence of steam-containing inert gas was proposed (Japanese Patent Publication No. 9368/1968). This method, however, imposes substantial limitations on the protection of apparatus against corrosion and the selection of apparatus material and adds complexity to reaction operation, leaving practical problems.